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<b><b>berkdb open</b></b>
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<b><pre>berkdb open
[-auto_commit]
[-btree | -hash | -recno | -queue | -unknown]
[-cachesize {gbytes bytes ncache}]
[-create]
[-delim delim]
[-dup]
[-dupsort]
[-encrypt]
[-encryptaes passwd]
[-encryptany passwd]
[-env env]
[-errfile filename]
[-excl]
[-extent size]
[-ffactor density]
[-len len]
[-mode mode]
[-nelem size]
[-pad pad]
[-pagesize pagesize]
[-rdonly]
[-recnum]
[-renumber]
[-snapshot]
[-source file]
[-truncate]
[-txn txnid]
[--]
[file [database]]
</pre></b>
<b>Description(berkdb open)</b>
<p>The <b>berkdb open</b> command opens and optionally creates a database.
The returned database handle is bound to a Tcl command of the form
<b>dbN</b>, where N is an integer starting at 0 (for example, db0 and
db1). It is through this Tcl command that the script accesses the
database methods.</p>
<p>The options are as follows:</p>
<br>
<b>-auto_commit</b><ul compact><li>Enclose the call within a transaction. If the call succeeds, the open
operation will be recoverable and all subsequent database modification
operations based on this handle will be transactionally protected. If
the call fails, no database will have been created.</ul>
<b>-btree</b><ul compact><li>Open/create a database of type Btree. The Btree format
is a representation of a sorted, balanced tree structure.</ul>
<b>-hash</b><ul compact><li>Open/create a database of type Hash. The Hash format is
an extensible, dynamic hashing scheme.</ul>
<b>-queue</b><ul compact><li>Open/create a database of type Queue. The Queue format
supports fast access to fixed-length records accessed by sequentially or
logical record number.</ul>
<b>-recno</b><ul compact><li>Open/create a database of type Recno. The Recno format
supports fixed- or variable-length records, accessed sequentially or by
logical record number, and optionally retrieved from a flat text file.</ul>
<b>-unknown</b><ul compact><li>The database is of an unknown type, and must already exist.</ul>
<b>-cachesize {gbytes bytes ncache}</b><ul compact><li>Set the size of the database's shared memory buffer pool (that is, the
cache), to <b>gbytes</b> gigabytes plus <b>bytes</b>. The cache
should be the size of the normal working data set of the application,
with some small amount of additional memory for unusual situations.
(Note: The working set is not the same as the number of simultaneously
referenced pages, and should be quite a bit larger!)
<p>The default cache size is 256KB, and may not be specified as less than
20KB. Any cache size less than 500MB is automatically increased by 25%
to account for buffer pool overhead; cache sizes larger than 500MB are
used as specified.</p>
<p>It is possible to specify caches to Berkeley DB that are large enough so that
they cannot be allocated contiguously on some architectures; for example,
some releases of Solaris limit the amount of memory that may be
allocated contiguously by a process. If <b>ncache</b> is 0 or 1, the
cache will be allocated contiguously in memory. If it is greater than
1, the cache will be broken up into <b>ncache</b> equally sized
separate pieces of memory.</p>
<p>For information on tuning the Berkeley DB cache size, see
<a href="../../db4-devel-4.7.25/ref/am_conf/cachesize.html">Selecting a cache size</a>.</p>
<p>Because databases opened within Berkeley DB environments use the cache
specified to the environment, it is an error to attempt to set a cache
in a database created within an environment.</p></ul>
<b>-create</b><ul compact><li>Create any underlying files, as necessary. If the files do not already
exist and the <b>-create</b> argument is not specified, the call will
fail.</ul>
<b>-delim delim</b><ul compact><li>Set the delimiting byte used to mark the end of a record in the backing
source file for the Recno access method.
<p>This byte is used for variable length records if the <b>-source</b>
argument file is specified. If the <b>-source</b> argument file is
specified and no delimiting byte was specified, <newline>
characters (that is, ASCII 0x0a) are interpreted as end-of-record
markers.</p></ul>
<b>-dup</b><ul compact><li>Permit duplicate data items in the tree, that is, insertion when the
key of the key/data pair being inserted already exists in the tree will
be successful. The ordering of duplicates in the tree is determined by
the order of insertion unless the ordering is otherwise specified by
use of a cursor or a duplicate comparison function. <p>error to specify both <b>-dup</b> and <b>-recnum</b>.</p></ul>
<b>-dupsort</b><ul compact><li>Sort duplicates within a set of data items. A default lexical
comparison will be used. Specifying that duplicates are to be sorted
changes the behavior of the <i>db</i> <b>put</b> operation as well as the
<i>dbc</i> <b>put</b> operation when the <b>-keyfirst</b>, <b>-keylast</b>
and <b>-current</b> options are specified.</ul>
<b>-encrypt</b><ul compact><li>Specify the database in an environment should be encrypted with the
same password that is being used in the environment.</ul>
<b>-encryptaes passwd</b><ul compact><li>Specify the database should be encrypted with the given password
using the Rijndael/AES (also known as the Advanced Encryption Standard
and Federal Information Processing Standard (FIPS) 197) algorithm.</ul>
<b>-encryptany passwd</b><ul compact><li>Specify the already existing database should be opened
with the given password. This option is used if the database is
known to be encrypted, but the specific algorithm used is not known.</ul>
<b>-env env</b><ul compact><li>If no <b>-env</b> argument is given, the database is standalone; that
is, it is not part of any Berkeley DB environment.
<p>If a <b>-env</b> argument is given, the database is created within the
specified Berkeley DB environment. The database access methods automatically
make calls to the other subsystems in Berkeley DB, based on the enclosing
environment. For example, if the environment has been configured to use
locking, the access methods will automatically acquire the correct locks
when reading and writing pages of the database.</p></ul>
<b>-errfile filename</b><ul compact><li><p>When an error occurs in the Berkeley DB library, a Berkeley DB error or an error
return value is returned by the function. In some cases, however, the
errno value may be insufficient to completely describe the cause of the
error especially during initial application debugging.</p>
<p>The <b>-errfile</b> argument is used to enhance the mechanism for
reporting error messages to the application by specifying a file to be
used for displaying additional Berkeley DB error messages. In some cases, when
an error occurs, Berkeley DB will output an additional error message to the
specified file reference.</p>
<p>The error message will consist of a Tcl command name and a colon (":"),
an error string, and a trailing <newline> character. If
the database was opened in an environment, the Tcl command name will be
the environment name (for example, env0), otherwise it will be the
database command name (for example, db0).</p>
<p>This error-logging enhancement does not slow performance or significantly
increase application size, and may be run during normal operation as well
as during application debugging.</p>
<p>For database handles opened inside of Berkeley DB environments, specifying the
<b>-errfile</b> argument affects the entire environment and is equivalent
to specifying the same argument to the <b>berkdb env</b> command.</p></ul>
<b>-excl</b><ul compact><li>Return an error if the database already exists.</ul>
<b>-extent size</b><ul compact><li>Set the size of the extents of the Queue database; the size is specified
as the number of pages in an extent. Each extent is created as a
separate physical file. If no extent size is set, the default behavior
is to create only a single underlying database file.</ul>
<p>For information on tuning the extent size, see
<a href="../../db4-devel-4.7.25/ref/am_conf/extentsize.html">Selecting a extent size</a>.</p>
<b>-ffactor density</b><ul compact><li>Set the desired density within the hash table.
<p>The density is an approximation of the number of keys allowed to
accumulate in any one bucket</ul>
<b>-len len</b><ul compact><li>For the Queue access method, specify that the records are of length
<b>len</b>.
<p>For the Recno access method, specify that the records are fixed-length,
not byte-delimited, and are of length <b>len</b>.</p>
<p>Any records added to the database that are less than <b>len</b> bytes
long are automatically padded (see the <b>-pad</b> argument for more
information).</p>
<p>Any attempt to insert records into the database that are greater than
<b>len</b> bytes long will cause the call to fail immediately and return
an error.</p></ul>
<b>-mode mode</b><ul compact><li><p>On UNIX systems, or in IEEE/ANSI Std 1003.1 (POSIX) environments, all files created by the access methods
are created with mode <b>mode</b> (as described in <b>chmod</b>(2)) and
modified by the process' umask value at the time of creation (see
<b>umask</b>(2)). The group ownership of created files is based on
the system and directory defaults, and is not further specified by Berkeley DB.
If <b>mode</b> is 0, files are created readable and writable by both
owner and group. On Windows systems, the mode argument is ignored.</p></ul>
<b>-nelem size</b><ul compact><li>Set an estimate of the final size of the hash table.
<p>If not set or set too low, hash tables will still expand gracefully as
keys are entered, although a slight performance degradation may be
noticed.</p></ul>
<b>-pad pad</b><ul compact><li>Set the padding character for short, fixed-length records for the Queue
and Recno access methods.
<p>If no pad character is specified, <space> characters (that is,
ASCII 0x20) are used for padding.</p></ul>
<b>-pagesize pagesize</b><ul compact><li>Set the size of the pages used to hold items in the database, in bytes.
The minimum page size is 512 bytes, and the maximum page size is 64K
bytes. If the page size is not explicitly set, one is selected based
on the underlying filesystem I/O block size. The automatically selected
size has a lower limit of 512 bytes and an upper limit of 16K bytes.
<p>For information on tuning the Berkeley DB page size, see
<a href="../../db4-devel-4.7.25/ref/am_conf/pagesize.html">Selecting a page size</a>.</p></ul>
<b>-rdonly</b><ul compact><li>Open the database for reading only. Any attempt to modify items in the
database will fail, regardless of the actual permissions of any
underlying files.</ul>
<b>-recnum</b><ul compact><li>Support retrieval from the Btree using record numbers.
<p>Logical record numbers in Btree databases are mutable in the face of
record insertion or deletion. See the <b>-renumber</b> argument for
further discussion.</p>
<p>Maintaining record counts within a Btree introduces a serious point of
contention, namely the page locations where the record counts are stored. In
addition, the entire tree must be locked during both insertions and
deletions, effectively single-threading the tree for those operations.
Specifying <b>-recnum</b> can result in serious performance degradation
for some applications and data sets.</p>
<p>It is an error to specify both <b>-dup</b> and <b>-recnum</b>.</p></ul>
<b>-renumber</b><ul compact><li>Specifying the <b>-renumber</b> argument causes the logical record
numbers to be mutable, and change as records are added to and deleted from
the database. For example, the deletion of record number 4 causes records
numbered 5 and greater to be renumbered downward by one. If a cursor was
positioned to record number 4 before the deletion, it will refer to the
new record number 4, if any such record exists, after the deletion. If a
cursor was positioned after record number 4 before the deletion, it will
be shifted downward one logical record, continuing to refer to the same
record as it did before.
<p>Using the <i>db</i> <b>put</b> or <i>dbc</i> <b>put</b> interfaces to create new records will
cause the creation of multiple records if the record number is more than one
greater than the largest record currently in the database. For example,
creating record 28 when record 25 was previously the last record in the
database, will create records 26 and 27 as well as 28.</p>
<p>If a created record is not at the end of the database, all records following
the new record will be automatically renumbered upward by one. For example,
the creation of a new record numbered 8 causes records numbered 8 and
greater to be renumbered upward by one. If a cursor was positioned to record
number 8 or greater before the insertion, it will be shifted upward one
logical record, continuing to refer to the same record as it did before.</p>
<p>For these reasons, concurrent access to a Recno database with the
<b>-renumber</b> flag specified may be largely meaningless, although it
is supported.</p></ul>
<b>-snapshot</b><ul compact><li>This argument specifies that any specified <b>-source</b> file be read
in its entirety when the database is opened. If this argument is not
specified, the <b>-source</b> file may be read lazily.</ul>
<b>-source file</b><ul compact><li>Set the underlying source file for the Recno access method. The purpose
of the <b>-source</b> file is to provide fast access and modification
to databases that are normally stored as flat text files.
<p>If the <b>-source</b> argument is give, it specifies an underlying flat
text database file that is read to initialize a transient record number
index. In the case of variable length records, the records are separated
as specified by <b>-delim</b>. For example, standard UNIX byte stream
files can be interpreted as a sequence of variable length records
separated by <newline> characters.</p>
<p>In addition, when cached data would normally be written back to the
underlying database file (for example, when the <i>db</i> <b>close</b> or
<i>db</i> <b>sync</b> commands are called), the in-memory copy of the database
will be written back to the <b>-source</b> file.</p>
<p>By default, the backing source file is read lazily, that is, records
are not read from the file until they are requested by the application.
<b>If multiple processes (not threads) are accessing a Recno database
concurrently and either inserting or deleting records, the backing source
file must be read in its entirety before more than a single process
accesses the database, and only that process should specify the backing
source argument as part of the <b>berkdb open</b> call. See the <b>-snapshot</b>
argument for more information.</b></p>
<p><b>Reading and writing the backing source file specified by <b>-source</b>
cannot be transaction protected because it involves filesystem
operations that are not part of the Berkeley DB transaction methodology.</b>
For this reason, if a temporary database is used to hold the records,
it is possible to lose the contents of the <b>-file</b> file, for
example, if the system crashes at the right instant. If a file is used
to hold the database, that is, a filename was specified as the
<b>file</b> argument to <b>berkdb open</b>, normal database recovery on
that file can be used to prevent information loss, although it is still
possible that the contents of <b>-source</b> will be lost if the system
crashes.</p>
<p>The <b>-source</b> file must already exist (but may be zero-length) when
<b>berkdb open</b> is called.</p>
<p>It is not an error to specify a read-only <b>-source</b> file when
creating a database, nor is it an error to modify the resulting database.
However, any attempt to write the changes to the backing source file using
either the <i>db</i> <b>close</b> or <i>db</i> <b>sync</b> commands will fail, of course.
Specify the <b>-nosync</b> argument to the <i>db</i> <b>close</b> command will
stop it from attempting to write the changes to the backing file; instead,
they will be silently discarded.</p>
<p>For all of the previous reasons, the <b>-source</b> file is generally
used to specify databases that are read-only for Berkeley DB applications,
and that are either generated on the fly by software tools, or modified
using a different mechanism such as a text editor.</p></ul>
<b>-truncate</b><ul compact><li>Physically truncate the underlying file, discarding all previous databases
it might have held. Underlying filesystem primitives are used to
implement this flag. For this reason, it is only applicable to the
physical file and cannot be used to discard databases within a file.
<p>The <b>-truncate</b> argument cannot be transaction-protected, and it is
an error to specify it in a transaction-protected environment.</p></ul>
<b>-txn txnid</b><ul compact><li>If the operation is part of an application-specified transaction, the
<b>txnid</b> parameter is a transaction handle returned from
<i>env</i> <b>txn</b>. If no transaction handle is specified, but the
-auto_commit flag is specified,
the operation will be implicitly transaction protected.</ul>
<b>--</b><ul compact><li>Mark the end of the command arguments.</ul>
<b>file</b><ul compact><li>The name of a single physical file on disk that will be used to back the
database.</ul>
<b>database</b><ul compact><li>The <b>database</b> argument allows applications to have multiple
databases inside of a single physical file. This is useful when the
databases are both numerous and reasonably small, in order to avoid
creating a large number of underlying files. It is an error to attempt
to open a second database file that was not initially created using a
<b>database</b> name.
<p>Applications opening multiple databases in a single file will almost
certainly need to create a shared database environment. See
<a href="../../db4-devel-4.7.25/ref/am/opensub.html">Opening multiple databases in a single
file</a> for more information.</p></ul>
<br>
<p>The <b>berkdb open</b> command returns a database handle on success.</p>
<p>In the case of error, a Tcl error is thrown.</p>
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